Vibration damping material and vibration damper

ABSTRACT

A vibration damping material ( 10 ) comprising a laminate consisting of two ( 20,40 ) metal sheets with a rubber layer ( 30 ) sandwiched therebetween, and another rubber layer ( 50 ) attached to either of the metal sheets, the rubber layers being made of solid rubber foil or rubber film produced by carrier calendaring and vulcanised to the metal sheets. One of the metal sheet properties influenceable by sound, vibration, and/or temperature, is different between the metal sheets. A vibration damper for application to a panel, which vibration damper is made from the vibration damping material.

The present invention relates to a vibration damping material andvibration dampers made from this material. The vibration dampersaccording to the invention are particularly useful in the automotiveindustry, for application to various panels, such as panels ofautomobile bodies, e.g. engine parts.

A known method of damping vibration of a panel having a large surfacearea relative to the thickness is to apply a viscoelastic dampingmaterial in sheet form to the panel. In the viscoelastic materialapplied to the panel, a large amount of the mechanical or kinetic energyput into the material under vibration is converted into heat energythrough molecular friction, and then dissipated.

Conventional vibration dampers for application to panels may beclassified into the following categories:

-   -   Free or unconstrained layer damping This is the simplest way of        introducing damping into a structure. This concept involves a        simple layer of an appropriate damping material bonded to those        surfaces of the structure which are vibrating. The damping        involves cyclic tension/compression deformation, resulting in        dissipation of energy.    -   Constrained layer damping. Variations of this concept are among        the most efficient ways of introducing damping into a structure.        Single constrained layer is the most familiar form of these        treatments. It consists of a thin layer of damping material        combined with a constraining layer of metallic foil or similar        rigid material. The damping mechanism involves cyclic shear        deformation of the damping material.

EP 0077987 discloses a constrained layer vibration damper in the form ofa three-layered laminate, which comprises a meltable bonding layer to bebrought into contact with a panel to be damped, a viscoelastic layer anda constraining layer laminated such that the viscoelastic layer isintimately sandwiched between the bonding layer and the constraininglayer. The constraining layer of this damper is formed of a resincomposition comprising an uncured thermosetting resin and an inorganicfiller. The viscoelastic layer is formed of a viscoelastic and adhesivematerial, and serves the function of damping or attenuating mechanicalvibrations and, besides, serves as an adhesive layer to bond theconstraining layer to the meltable bonding layer. The viscoelastic layercan be provided by using a double-faced adhesive tape produced bycoating both sides of a thin plastic film with a viscoelastic adhesive.Regarding the constraining layer, metals are explicitly excluded, as itis said in EP 0077987 that a metal constraining layer would make itdifficult to bring the damper into dose contact with an intricatelyshaped panel.

U.S. Pat. No. 5,407,034 (Vydra) discloses a prior art damping structureincluding damping layers of viscoelastic material alternating with anouter metal layer, a middle metal layer and an inner metal layer. Thelayers are said to be bonded together in a suitable manner. Adisadvantage of the disclosed prior art is said to be that the dampinglayer is subjected to significant torsional and rotational forces whichcan degrade it and impair noise-damping effectiveness. Furthermore, theprior art provides insufficient noise damping at lower frequencies.Vydra's solution to this problem is a brake pad assembly comprising abrake shoe structure including a rigid backing structure and a frictionlining pad carried by it. The backing structure has a plurality ofperforations and includes a rigid imperforate backing plate. A dampingplate with perforations is fixed to the backing plate, and metalconstraining layers are disposed along the opposite sides of the dampingplate. Viscoelastic damping material is disposed in the perforations.The disclosed prior art, as well as Vydra's invention, comprise rigidplates, which is necessary in order to make the damping structure endurethe forces applied by the brake piston. This means that the structure isnot fit to be plastically shaped.

It has now been found that improved damping can be obtained by means ofa vibration damping material as defined in appended claim 1. Moreparticularly, the present vibration damping material comprises alaminate consisting of a first and a second thin metal sheet and a firstrubber layer sandwiched therebetween, wherein said first rubber layer isa solid rubber foil or rubber film produced by carrier calendaring andvulcanised together with each of said metal sheets, and a second rubberlayer, which is a solid rubber foil or rubber film produced by carriercalendaring, that is vulcanised together with said first or second metalsheet.

Preferably, said first rubber layer is thinner than about 0.5 mm, and inparticular, it may have a thickness of about 0.1-0.08 mm.

The second rubber layer is preferably made as thin as possible. In apreferred case, it has a thickness of about 0.5 mm or less.

Said first metal sheet preferably has a thickness of about 0.3-1.5 mm.

Said second metal sheet preferably has a thickness of about 0.3-1.5 mm.

The metal sheets may be made of any suitable metal, although they arepreferably made of carbon steel or aluminium.

The total bending stiffness of the laminate should preferably correspondto between about ⅓ to about {fraction (1/1)} of the bending stiffness ofthe panel to be dampened.

In a preferred case, one or more of the metal sheet propertiesinfluenceable by sound, vibration, and/or temperature, is/are differentbetween the first and the second metal sheet.

The rubber layers may be made of any suitable elastomer, although theyare preferably made of nitrile or butyl rubber.

The rubber layers may be made electrically conductive, for instance byadding carbon black in effective quantities to the mixture prior to thecalendaring process, as is known in the art. The use of electricallyconductive rubber layers enables the material to be welded, e.g.spot-welded, for simple and effective adaptation, including jointing.

The rubber layer of the inventive laminated material has the smallestpossible porosity. Thus, the rubber layer has those specific propertiesand the unique structure exhibited by carrier calendared rubber films.Among other things, there is obtained a homogeneity and evenness withregard to both physical properties and dimensions. For instance, therubber layer shall be as free from pores to the greatest possibleextent, a property which cannot be achieved with a rubber layer that hasbeen applied in the form of a solution or paste and which has beenrolled or pressed directly onto or between the metal sheets. Such rubberlayers will always contain paste-forming residues or solvent residuesthat generate pore formations and other inhomogenities and thereby giverise to weakening zones, which also occur in any glue layers present.The rubber films should be applied to the metal sheet with the aid of acarrier used in the calendaring process, this carrier ensuring highlyeffective and primarily flat abutment with the surface of the metalsheet in the absence of tendencies to forming irregularities in theabutment surfaces. These conditions also enable vulcanisation of therubber layer to the metal sheet to be effected readily with regard tothe strength of the rubber-metal sheet bond.

Although the present vibration damping material may be attached to thepanel to be dampened by way of gluing in situ, i.e. by supplying aseparate adhesive at the time of applying the material to the panel, thepresent vibration damping material preferably comprises a layer ofadhesive, applied to the surface of the second rubber layer facing awayfrom the said first and second metal sheets.

The vibration damping material may be manufactured in accordance withthe method described in WO 91/13758, which method involves the use of adisposable carrier in the production of rubber foil or rubber film bycalendaring and subsequent vulcanisation in a belt vulcanising machine.When the rubber layer is produced in accordance with this method, therubber foil or film thus formed obtains an homogeneity and evenness withregard to both its physical properties and its dimensions as indicatedin the foregoing, for instance a very low porosity. Because the rubberlayer is applied to the first metal sheet with the aid of a carrier,very effective and primarily flat abutment is ensured with the metalsheet surface with no tendencies towards irregularities in the abuttingsurfaces. The rubber coated first sheet can then be readily applied tothe second metal sheet, because the first metal sheet functions as astable carrier in this stage of manufacture. With these conditions, therubber foil or rubber film can be vulcanised readily to both plateswithout problems concerning the mechanical strength of the rubber-metalsheet joints. The method of belt vulcanising in two stages is describedin WO 93/13329.

The inventive material can, in principle, be handled and treated asthough it were a metal plate and is plastically shaped and worked atleast in a cold state by curving, bending, drawing, stretching, orpressing the material or subjecting said material to similar treatment,without the material loosing its vibration damping properties. This isbecause the material behaves as a homogenous product in this context,despite being a laminate. The reasons for this are because the rubberlayer is solid and homogeneously produced by carrier calendaring, andbecause the layer is vulcanised directly onto the metal sheets in theabsence of any binder layer which would otherwise create weak zones whenshaping or working the material. The material thus exhibits no cracks orinhomogenities in the joint between the rubber-metal boundary surfaces,not even when the material is deformed when being worked. This is thereason why the material was found to exhibit good properties in testscarried out on the material. Vulcanisation of a solid rubber film to themetal sheets results in an homogenous structure and a firm bond acrossthe whole surface of contact between the rubber layer and the metalsheet, and therewith in uniform damping properties.

The present invention also relates to a vibration damper for applicationto a panel to damp vibrations of the panel, which vibration damper ismade from the present vibration damping material.

The present invention is useful for damping various automotive partssuch as, for instance, oil pans, engine housings, cam housings, chaindrive housings, and in particular housings made of aluminium.

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1 is a diagrammatic cross section through a vibration damperlaminate material according to one embodiment of the present invention;

FIG. 2 is a graph showing Loss Factor variation with temperature, atvarious frequencies, for one embodiment of the invention; and

FIG. 3. is a graph showing Young's modulus variation with temperature,at various frequencies, for one embodiment of the invention.

In FIG. 1, in which the dimensions of the various layers have not beenshown to scale, it will be apparent that the laminate material 10 cancomprise a pair of metal plates 20 and 40 acting as constraining layers,between which a web 30 acting as a constrained layer, previously formedof rubber is sandwiched so that these sheets coat the elastomer core. Asecond web 50 also acting as a constrained layer, of rubber is bonded tothe opposite side of metal plate 40. A layer 60 of pressure adhesive isapplied on top of rubber web 50. The purpose of this pressure adhesivelayer 60 is to bond dampers made of the vibration damper laminatematerial to various panels, such as the panels of automobile bodies,e.g. engine parts, the vibrations of which are to be damped. Beforebeing applied and bonded accordingly, the pressure adhesive layer 60 isprotected by a plastic protection 70.

EXAMPLE

A vibration damper laminate was made from a metal-rubber-metal-rubberlaminate constructed in accordance with the invention. The laminatecomprised of 1.0 mm galvanised carbon steel—0.1 mm nitrile rubber—1.0 mmgalvanised carbon steel—0.3 mm nitrile rubber. Loss factor for thelaminate was measured according to the international standard ASTM E-75698, which is a mechanical impedance procedure. The material was cut in12.7 mm wide and 255 mm long samples, which were bonded to a bare steelbasebeam. The beam was placed in a fixture including a non-touchexciter, which induces vibrations at the end of the cantilever beam. Thebasebeam was 2.93 mm thick, 12.7 mm wide and had a free length of 255 mmwhen placed in the fixture. The test was performed in an environmentalchamber with a temperature range of −35° C. to 180° C., at frequenciesof 500, 1000, and 3000 Hz. The measurement results are set forth in FIG.1, which shows the material loss factor values as function oftemperature after reduction of the basebeam, and FIG. 2, which shows theYoung's modulus for the same beam as function of temperature.

1. A vibration damping material (10) comprising a laminate consisting ofa first (20) and a second (40) metal sheet with a first rubber layer(30) sandwiched therebetween, and a second rubber layer (50) attached toeither of said first or second metal sheets, characterised in that therubber layers are solid rubber foil or rubber film produced by carriercalendaring and are vulcanised together with the respective metal sheet,and in that one or more of the metal sheet properties influenceable bysound, vibration, and/or temperature, is/are different between the firstand the second metal sheet.
 2. A vibration damping material according toclaim 1, characterised in that it comprises a layer (60) of adhesiveapplied to the surface of the second rubber layer that faces away fromthe said first and second metal sheets.
 3. A vibration damper forapplication to a panel to damp vibrations of the panel, characterised inthat said vibration damper is made from a vibration damping materialcomprising a laminate consisting of a first and a second metal sheetwith a first rubber layer sandwiched therebetween, and a second rubberlayer attached to either of said first or second metal sheets, whereinthe rubber layers are solid rubber foil or rubber film produced bycarrier calendaring and are vulcanised together with the respectivemetal sheet, and in that one or more of the metal sheet propertiesinfluenceable by sound, vibration, and/or temperature, is/are differentbetween the first and the second metal sheet.
 4. A vibration damperaccording to claim 3(4), characterised in that it comprises a layer ofadhesive applied to the surface of the second rubber layer, which layerof adhesive faces away from the said first and second metal sheets.
 5. Avibration damper according to claim 3(4), characterised in that thetotal bending stiffness of the laminate corresponds to between about ⅓to about {fraction (1/1)} of the bending stiffness of the panel to bedampened.